1. Field of the Invention
The present invention relates to a promoter participating in expression of the function of a structural gene as one moiety or site of a DNA of the gene. More specifically, the present invention relates to a plant-derived promoter.
2. Description of the Prior Art
A promoter is a site of a DNA where an RNA polymerase begins transcription upon being thereon, and the presence of this site is indispensable for expression of a structural gene in an operon to which it belongs.
Analysis of genes has been made mainly on procaryon organisms or procaryotes such as bacteria and phages, particularly bacteria, especially Escherichia coli. Hence, promoters of procaryotes have been mainly examined, and many promoters such as a promoter of lac (lactose operon of E. coli), a promoter of trp (tryptophan operon of E. coli), and a promoter of ara (arabinose operon of E. coli) are known.
It is generally considered that a promoter of a eucaryotic cell does not act in a procaryotic cell, and if a procaryote is used as a host in transformation or the like, it is necessary to use a promoter of a procaryote such as a bacterium or phage.
In contrast to the above general knowledge, we have already found that a fraction having a size of about 5.1 kbp among fractions obtained by digestion by or with Eco. RI of a chloroplast DNA of Marchantia polymorpha L. that is classified as a eucaryote acts as a promoter in E. coli that is a procaryote (8th Symposium of Tissue Culture of Plants). The term "fraction" is herein used interchangeably with a term "fragment".
The intensity of the promoter, that is, the frequency of transcription in forming a RNA from a DNA, or the activity of the promoter, differs with the kind of the promoter, and when DNA containing a promoter is used as a vector for molecular breeding, a promoter having a higher activity is advantageous. Furthermore, since a passenger, namely an exogenous DNA, is integrated in the vector, it is preferable that the size of the promoter be small. Accordingly, a DNA containing a promoter of a small size is easy to use and handle. Therefore, development of a new promoter is always desired.